Evolution of the semiconductor manufacturing industry is placing ever greater demands on yield management and, in particular, on metrology and inspection systems. Critical dimensions are shrinking while wafer size is increasing. Economics is driving the industry to decrease the time for achieving high-yield, high-value production. Thus, minimizing the total time from detecting a yield problem to fixing it determines the return-on-investment for the semiconductor manufacturer.
Wafers can be inspected using a variety of techniques typically based on optical methods or scanning electron microscopes (SEM). Previously, broad band plasma (BBP) attributes were used to determine SEM inspection sampling. Metrology inputs were not used.
As design nodes continue to shrink, the optical signal-to-noise ratio for subtle failures of hotspots is becoming a more challenging issue. A hot inspection (e.g., an inspection in which a threshold for determining presence of a potential defect is substantially close to a noise floor of the inspection) can be run and then various attributes of captured defects can be used to perform an elaborate sample for SEM verification. However, this can be an extremely expensive technique. Although a hot inspection can increase the likelihood of detecting defects of interest, it is at the expense of substantially high nuisance rates. Less than 5,000 defects may be sampled from over one million defects detected by optical inspection. These process variations typically occur as a function of wafer level or exposure field level fluctuations. There also are limited possibilities of guided SEM review or SEM inspection without optical inspection because there is limited information about which wafer/field areas to look into.
Therefore, improved techniques and systems for SEM inspection and review are needed.